Titanocene dichloride is a valuable reagent for inorganic and organic chemistry. For example, titanocene dichloride is employed in the preparation of dimethyl titanocene (U.S. Pat. No. 5,892,082; PCT Patent Publication WO 97/09336) which is an effective methylenating reagent for a variety of carbonyl compounds, including esters and lactones (N. A. Petasis and E. I. Bzowej, J. Am. Chem. Soc., 112, 6392-6394 (1990); U.S. Pat. No. 5,087,790). It is well recognized in the art that dimethyl titanocene has become a useful synthetic tool. See for example the extensive use of dimethyl titanocene by e.g., N. A. Petasis and M. A. Patane, Tetrahedron Lett., 31, 6799 (1990); P. DeShong and P. J. Rybczynski, J. Org. Chem., 56, 3207 (1991); J. S. Swenton, D. Bradin, B. D. Gates, J. Org. Chem., 56, 6156 (1991); N. A. Petasis and E. I. Bzowej, Tetrahedron Lett., 34, 1721 (1993); H. K. Chenault and L. F. Chafin, J. Org. Chem., 59, 6167 (1994); D. Kuzmich, S. C. Wu, D.-C. Ha, C.-S. Lee, S. Ramesh, S. Atarashi, J.-K. Choi and D. J. Hart, J Am. Chem. Soc., 116, 6943 (1994).
In conducting such methylenating reactions a stochiometric amount of dimethyl titanocene is employed, thereby requiring the purchase of stochiometric amounts of titanocene dicloride to prepare the dimethyl titanocene. Furthermore, a by-product of methylenating carbonyl compounds, such as esters and lactones, with dimethyl titanocene is the titanocene dimer (Cp.sub.2 Ti(CH.sub.3)).sub.2 O for which proper disposal must be arranged.
Accordingly, there is a need in the art for a more economical and efficient method for the preparation of titanocene dichloride. The present invention provides a more economical method for the preparation of titanocene dichloride in high yield from dimethyl titanocene dimer (Cp.sub.2 Ti(CH.sub.3)).sub.2 O and hydrogen chloride. The present process is readily amenable to the recycling of titanocene dichloride on a large scale.